The present invention is directed to polishing pads used for creating a smooth, ultra-flat surface on such items as glass, semiconductors, dielectric/metal composites, magnetic mass storage media and integrated circuits. More specifically, the invention is directed to a pad comprised of a thermoplastic foam substrate and having a surface comprised of concave cells with a polishing agent coating the interior surface of the concave cells.
Chemical-mechanical polishing (CMP) is used extensively as a planarizing technique in the manufacture of VLSI integrated circuits. It has potential for planarizing a variety of materials in IC processing but is used most widely for planarizing metallizied layers and interlevel dielectrics on semiconductor wafers, and for planarizing substrates for shallow trench isolation.
In shallow trench isolation (STI), for example, large areas of field oxide must be polished via to produce a planar starting wafer. Achieving acceptable planarization across the full diameter of a wafer using traditional etching processes has been largely unsuccessful. However, using conventional CMP, where the wafer is polished using a mechanical polishing wheel and a slurry of chemical etchant, unwanted oxide material is removed with a high degree of planarity.
Similarly, multilevel metallization processes, each level in the multilevel structure contributes to irregular topography. Planarizing interlevel dielectric layers, as the process proceeds, is often now favored in many state-of-the-art IC fabrication processes. High levels of planarity in the metal layers is a common objective, and this is promoted by using plug interlevel connections. A preferred approach to plug formation is to blanket deposit a thick metal layer, comprising, for example W, Ti, TiN, on the interlevel dielectric and into interlevel windows, and then removing the excess metal using CMP. CMP may also be used for polishing an oxide layers, such as SiO2, Ta2O5 or W2O5 or to polish nitride layers such as Si3 N4, TaN, TiN.
There are, however, several deficiencies in conventional polishing pad materials. Various types of materials, such as polyurethane, polycarbonate, nylon, polyureas, felt, or polyester, have poor inherent polishing ability, and hence are not used as polishing pads in their virgin state. In certain instances, mechanical or chemical texturing may transform these materials, thereby rendering them useful in polishing. Moreover, certain materials, such as polyurethane based pads, are decomposed by the chemically aggressive processing slurries by virtue of the inherent chemical nature of urethane. In turn, decomposition produces a surface modification in and of itself in the case of the polyurethane pads which may be detrimental to uniform polishing. In other instances, surface modification of materials used for CMP polishing pads may improve the application performance. Such modifications, however may be temporary, thus requiring frequency replacement or re-treatment of the CMP pad.
Accordingly, what is needed is an improved CMP pad capable of providing a highly planar surface during CMP and having improved longevity, while not experiencing the above-mentioned problems.
To address the above-discussed deficiencies, the present invention provides, in one embodiment, a polishing pad comprising a thermoplastic foam substrate having a surface comprised of concave cells and a polishing agent coating an interior surface of the concave cells. Another embodiment of the present invention is directed to a method for preparing a polishing pad. The method comprises the steps of providing a thermoplastic foam substrate, exposing cells with the substrate to form a surface comprising concave cells and coating an interior surface of concave cells with a polishing agent.
In yet another embodiment, the present invention provides a polishing apparatus. The apparatus comprises a mechanically driven carrier head, a polishing platen and a polishing pad. The carrier head is positionable against the polishing platen to impart a polishing force against the polishing platen. The polishing pad is attached to the polishing platen and includes a polishing body. The polishing body comprises a thermoplastic foam substrate having a surface comprised of concave cells and a polishing agent coating an interior surface of the concave cells.
The foregoing has outlined preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiments as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the scope of the invention.